<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>

</body>
<script>
    var array = [1,false, [1,2,3], () => {}]

    console.log(Array.isArray(array))

    array['hello'] = 1
    console.log(Array.isArray(array),array.length)
    console.log(array)
</script>
</html>